xe2x80x9cThis application is a national phase of PCT/FR01/02378 which was filed on Jul. 20, 2001, and was not published in English.xe2x80x9d
The subject of this invention is a microwave applicator that has the specific function of making a microwave beam output from a wave guide converge approximately at a point. One essential application of these appliances is superficial scarification of concrete in order to remove a crust that could be contaminated; the microwaves converge under this crust and generate sufficient local heating to evaporate the water contained in the concrete and apply a pressure that makes the crust crumble. The applicator can then be moved along parallel lines to produce striations on the concrete surface. French patent 2 759 239 proposed a solution to obtain this convergence of microwaves starting from an unfocussed divergent beam at the exit from a wave guide; the applicator comprised an envelope with an ellipsoid shaped internal surface reflecting the microwaves, the microwave guide ends at the bottom of the envelope, and the envelope comprised an opening at the opposite end of this bottom part facing the concrete surface, and a central reflector placed in the envelope around the first focal point of the ellipsoid and with a face reflecting microwaves and directed towards the bottom of the envelope. This arrangement was derived from the concept of using the geometric properties of an ellipse and particularly that a wave reflected firstly through one focal point and then by the contour of an ellipse necessarily reaches the second focal point. Thus, the reflecting envelope was in the shape of a portion of an ellipse and the central reflector was located at the first focal point of this ellipse and had an approximately circular shape to reproduce reflection at a point as accurately as possible. Radiation reflected firstly by the central reflector and then by the envelope left the envelope and actually converged at the second focal point of the ellipse under the concrete crust. It was intended to focus at a point with an ellipsoid shaped envelope and a spherical reflector, or on a linexe2x80x94which was preferable in practice in order to scarify the concrete in wide stripsxe2x80x94if the envelope was formed of elliptical sections similar to each other and if the central reflector was cylindrical.
However, this applicator was not sufficient since the central portion of the microwave beam emitted parallel to the wave guide was reflected on part of the central reflector that was normal to it, so that it was returned to the microwave guide and did not reach its destination. The purpose of the invention is to overcome this disadvantage and to make all microwaves participate in increasing the temperature of the convergence focal point.
According to the invention, the applicator comprises an envelope with a reflecting inside surface with a bottom and opening opposite each other, the microwave guide opening up in the bottom of the envelope, and a central reflector located in the envelope and comprising one face facing the microwave guide and profiled such that the microwaves are reflected by the inner face of the reflector and then by the inner face of the envelope converging approximately towards a focal point located in front of the opening of the envelope, characterised in that the said face of the central reflector comprises a first central facet and a second side facet on each side of the microwave guide, and the inner face of the envelope comprises a first central facet, a second facet and then a third facet on each side of the microwave guide, the facets being modelled such that a first portion of the microwaves reaches the focal point after being reflected by the second facet of the central reflector and then the second facet of the envelope, and a second portion of the microwaves reaches the focal point after having been reflected by the first facet of the central reflector, the first facet of the envelope and then the third facet of the envelope.
The most innovative element of the invention is therefore that the central portion of the radiation is reflected three times on the envelope before reaching the focal point.
Some particular shapes of facets may be proposed; thus, the second facet of the central reflector may be curved and convex and the second facet of the envelope may be elliptical; or the first facet of the central reflector may be plane, the first facet of the envelope may be circular and concave, and the third facet of the envelope may be plane.